1. Field of the Invention
This invention relates generally to a method of and apparatus for operation of a wireless communications system, and more specifically to methods of and apparatuses for increasing communication capacity through frequency re-use planning particularly for wireless communications systems using wireless translating repeaters.
2. Background of the Invention
A conventional wireless communications network 800 is shown in FIG. 8. As illustrated in FIG. 8, the wireless communications network 800 includes a plurality of cells 810a, 810b, a mobile unit 820, a plurality of base station transceivers (BTS) 805a, 805b, communication lines 840, a mobile telecommunications switching office (MTSO) 830, an interface 850, and a public switched telephone network (PSTN) 860.
The wireless communications network 800 has a fixed number of channel sets distributed among the BTS 805a, 805b serving a plurality of cells 810a, 810b arranged in a predetermined pattern. The mobile unit 820, in a cell 810a or 810b, communicates with the BTS 805a or 805b, respectively, via radio frequency (RF) means. The BTS 805a, 805b communicate with the MTSO 830 via communication lines 840. The MTSO 830 communicates with the switched telephone network 860 via the interface 850.
In the conventional wireless communications network 800, the cell areas typically range from 1 to 300 square miles. The larger cells typically cover rural areas, and the smaller cells typically cover urban areas. Cell antenna sites utilizing the same channel sets are spaced by a sufficient distance, e.g., typically referred to as the xe2x80x9creuse distancexe2x80x9d, to assure that co-channel interference is held to an acceptably low level.
The mobile unit 820 in a cell 810a has radio telephone transceiver equipment which communicates with similar equipment in BTS 805a, 805b as the mobile unit 820 moves from cell to cell.
Each BTS 805a, 805b relays telephone signals between mobile units 820 and a mobile telecommunications switching office (MTSO) 830 by way of the communication lines 840.
The communication lines 840 between a cell site, 810a or 810b, and the MTSO 830, are typically T1 lines. The T1 lines carry separate voice grade circuits for each radio channel equipped at the cell site, and data circuits for switching and other control functions.
The MTSO 830 in FIG. 8 includes a switching network (not shown) for establishing call connections between the public switched telephone network (PTSN) 860 and mobile units 820 located in cell sites 810a, 810b and for switching call connections from one cell site to another. In addition, the MTSO 830 includes a dual access feeder (not shown) for use in switching a call connection from one cell site to another. Various handoff criteria are known in the art and utilize features such as delay ranging to indicate the distance of a mobile unit from a receiving cell site, triangulation, and received signal strength to indicate the potential desirability of a handoff. Also included in the MTSO 830 is a central processing unit (not shown) for processing data received from the cell sites and supervisory signals obtained from the switched telephone network 860 to control the operation of setting up and taking down call connections.
The BTS 805a or 805b provides coverage for multiple subscribers in a specific cell, e.g., 810a or 810b. As the mobile unit 820 enters a cell, the BTS 805a or 805b and the mobile unit 820 communicate with one another. Information from this initial exchange is used by the cellular communication system 800 so that it can route calls to and from the mobile unit 820.
The BTS 805a or 805b has a limited coverage area. As a result, one technique for providing coverage for a large geographic area is to install multiple BTS units. Multiple BTS units are installed to provide coverage for a large geographic area. This strategy also provides the benefit of increasing capacity, so that the cellular system 800 can serve a larger number of subscribers within its coverage area. However, a major drawback to this solution is the high cost of a BTS. As an alternative, a repeater is often used to improve coverage area, reduce cost, and to improve clarity.
Generally, repeaters receive a downlink signal from a BTS and retransmit the downlink signal to a mobile unit after the downlink signal has been amplified by a downlink amplifier. The process works similarly in reverse, where the repeater will amplify an uplink signal from a mobile unit to the BTS with an uplink amplifier. The amplifiers provide an increase in signal strength which improves the clarity of the calls and prevents dropped calls. To distinguish the direction of the signals transmitted and received by the repeaters, the path between the repeater and the BTS is referred to as the xe2x80x9cbackhaulxe2x80x9d signal path.
Unfortunately, while the wireless repeaters thus far described provide a relatively large RF coverage area at a relatively low cost and without the need for a wireline backhaul, the operators of the prior art wireless communications networks must pay a penalty in available communication frequency as conventional wireless communications networks would have less number of available communications channels as a result of the addition of the repeaters.
Operators of wireless communications network must provide communications services to increasing number of subscribers using a limited available RF bandwidth. For example, each of operators of wireless systems, e.g., one based on the GSM-1900 standard, may be licensed to use only a total bandwidth of, e.g., 5 MHz to provide communications services to its subscriber.
Each communication channel of conventional wireless communications network, utilizing, e.g., the Gaussian Minimum Shift Keying (GMSK) modulated waveforms in, e.g., GSM-1900, GSM-1800 and GSM-900 standards, occupies 200 KHz of bandwidth. Moreover, because, e.g., according to the GSM standards, signal level from an adjacent channel must at least 9 dB below the desired signal level of a channel, in a conventional wireless communications network, center frequencies of any two adjacent channels must be at least 400 kHz apart from each another.
Thus, in a conventional wireless communication network having a 5 MHz of available RF bandwidth may be afforded at most 12 RF carrier channels (e.g., 5 MHz/400 kHz). The number of available carrier channels is further reduced when repeaters are employed in the network because communication via a repeater requires two rather than one channel to accommodate both the xe2x80x9clocalxe2x80x9d communications, e.g., between the repeaters and the mobile units, and the xe2x80x9cbackhaulxe2x80x9d communications, e.g., between the BTS and the repeaters.
For example, as shown in FIG. 9, a wireless communications network having one local cell A, and 5 repeaters B, C, D, E, and F, may utilize every other available frequency carrier channels, and thus would only be afforded 6 carrier channels 1, 3, 5, 7, 9, 11, and 13 (e.g., half of a network without repeaters), and thus may only have a total of 6 cells that may be served by a BTS.
Furthermore, if an operator of a conventional wireless communications network desires to have more available channels, then the operator must reduce the number of repeaters, thus also reducing the coverage area. Thus, in a conventional wireless communications network, a trade-off between efficient utilization of available RF bandwidth and larger coverage area usage must be made.
Accordingly, there is a need in the art for frequency planning that allows the maximum usage of the available RF bandwidth of a wireless communications network while at the same time affording an operator of the network the benefit of employing repeaters for larger coverage area.
An object of the present invention is to provide the maximum efficiency in RF bandwidth utilization in a wireless communications network.
Another object of the present invention is to increase the number of available RF communication channels without reducing the coverage area of a BTS in a wireless communications network.
Another object of the present invention is to provide a method for maximizing coverage area of a BTS in a wireless communications network.
It is yet another object of the present invention to provide a cost-effective means for increasing coverage area without reducing the number of available RF communication channels in a wireless communications network having a limited total RF bandwidth.
According to the principles of the present invention, a wireless communications network having an available radio frequency bandwidth divided into a plurality of radio frequency communication channels comprises a base transceiver system in communication with at least one subscriber in a coverage area arranged in a plurality of geographic cells, and at least one repeater having at least one ground wireless communication channel and at least one backhaul wireless communication channel, said at least one ground communication channel being operative to provide communication between said at least one repeater and said at least one subscriber, said at least one backhaul communication channel enabling communication between said base transceiver system and said at least one repeater, wherein at least two of said plurality of radio frequency communication channels adjacent to each other in a frequency spectrum are utilized by said wireless communications network for communications between at least two of said base transceiver system, said at least one repeater and said at least one subscriber.
According to the principles of the present invention, a method of assigning a plurality of communication channels of an available radio frequency bandwidth in a wireless communications network comprises assigning at least a first one of said plurality of communication channels for communication between a repeater and a subscriber of said wireless communications network, assigning at least a second one of said plurality of communication channels for communication between said repeater and a base transceiver system, said at least first one of said plurality of communication channels being adjacent in a frequency spectrum to said second one of said plurality of communication channels.